Magneto-optical defect sensor with common rf and magnetic fields generator

ABSTRACT

Systems and apparatuses are disclosed for providing a uniform RF field and magnetic bias field to a nitrogen vacancy center diamond.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent application Ser. No. 15/003,298, filed Jan. 21, 2016, and the contents of which are incorporated herein by reference in its entirety.

FIELD BACKGROUND

The present invention relates generally to a sensor assembly of a magnetic sensor.

Magnetic sensors based on a nitrogen vacancy (NV) center in diamond are known. Diamond NV (DNV) sensors may provide good sensitivity for magnetic field measurements. Such magnetic sensor systems often include components such an optical excitation source, an RF excitation source, and optical detectors. These components are all formed on different substrates or as separate components mechanically supported together.

SUMMARY

Systems and apparatuses are described that use multiple radio frequency elements for providing a uniform magnetic field over an NV diamond and also providing a magnetic bias for the NV diamond. In one implementation, a magnetic field sensor assembly includes four side radio frequency (RF) elements. Each side RF element includes an RF connection. The magnetic field sensor also includes four side RF feed cables connected to one of the four side RF elements such that each side RF element is connected to one RF feed cable that provides a feed signal to the side RF element. The magnetic field sensor also includes a top RF element and a bottom element along with a top RF element feed cable and a bottom RF feed cable. The top and bottom feed cables provide a RF feed signal to the top and bottom RF elements respectively. The four side RF side elements, the top RF element, and the bottom RF element are arranged in a cube formation. A nitrogen-vacancy (NV) center diamond is located within the cube formation. The side RF elements, top RF element, and bottom RF element generate a microwave signal that is uniform over the NV center diamond, and also generate a magnetic bias field to the NV center diamond.

In other implementations, a magnetic field sensor assembly includes four side radio frequency (RF) elements. Each side RF element includes an RF connection. The magnetic field sensor also includes four side RF feed cables connected to one of the four side RF elements such that each side RF element is connected to one RF feed cable that provides a feed signal to the side RF element. The magnetic field sensor also includes a top RF element and a bottom element along with a top RF element feed cable and a bottom RF feed cable. The top and bottom feed cables provide a RF feed signal to the top and bottom RF elements respectively. The four side RF side elements, the top RF element, and the bottom RF element are arranged in a column formation. A nitrogen-vacancy (NV) center diamond is located within the column formation. The side RF elements, top RF element, and bottom RF element generate a microwave signal that is uniform over the NV center diamond, and also generate a magnetic bias field to the NV center diamond.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

FIG. 1 illustrates one orientation of an NV center in a diamond lattice.

FIG. 2 is an energy level diagram illustrates energy levels of spin states for the NV center.

FIG. 3 is a schematic illustrating an NV center magnetic sensor system.

FIG. 4 is a graph illustrating the fluorescence as a function of applied RF frequency of an NV center along a given direction for a zero magnetic field and a non-zero magnetic field.

FIG. 5 is a graph illustrating the fluorescence as a function of applied RF frequency for four different NV center orientations for a non-zero magnetic field.

FIG. 6 is a schematic illustrating an NV center magnetic sensor system in accordance with some illustrative implementations.

FIG. 7 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIG. 8 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIGS. 9A and 9B are schematics illustrating a coil assembly in accordance with some illustrative implementations.

FIG. 10 is a cross section illustrating a coil assembly in accordance with some illustrative implementations.

FIG. 11 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

FIG. 12 is a schematic illustrating a top or bottom element of a coil assembly in accordance with some illustrative implementations.

FIG. 13 is a schematic illustrating a center mounting block of a coil assembly in accordance with some illustrative implementations.

FIG. 14 is a cross section illustrating of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIG. 15 is a schematic illustrating a coil assembly in accordance with some illustrative implementations.

FIG. 16 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations.

FIG. 17 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

FIG. 18 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIG. 19 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIG. 20 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

FIG. 21 is a schematic illustrating a coil assembly in accordance with some illustrative implementations.

FIG. 22 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations.

FIG. 23 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

FIGS. 24A and 24B are schematics illustrating top and bottom elements of a coil assembly in accordance with some illustrative implementations.

DETAILED DESCRIPTION

Nitrogen-vacancy (NV) centers are defects in a diamond's crystal structure. Synthetic diamonds can be created that have these NV centers. NV centers generate red light when excited by a light source, such as a green light source, and microwave radiation. When an excited NV center diamond is exposed to an external magnetic field the frequency of the microwave radiation at which the diamond generates red light and the intensity of the light change. By measuring this change and comparing the change to the microwave frequency that the diamond generates red light at when not in the presence of the external magnetic field, the external magnetic field strength can be determined. Accordingly, NV centers can be used as part of a magnetic field sensor.

In various implementations, microwave RF excitation is needed in a DNV sensor. The more uniform the microwave signal is across the NV centers in the diamond the better and more accurate an NV sensor will perform. Uniformity, however, can be difficult to achieve. Also, the larger the bandwidth of the element, the better the NV sensor will perform. Large bandwidth, such as octave bandwidth, however, can be difficult to achieve. Various NV sensors respond to a microwave frequency that is not easily generated by RF antenna elements that are comparable to the small size of the NV sensor. In addition, RF elements should reduce the amount of light within the sensor that is blocked by the RF elements. When a single RF element is used, the RF element is offset from the NV diamond when the RF element maximized the faces and edges of the diamond that light can enter or leave. Moving the RF element away from the NV diamond, however, impacts the uniformity of strength of the RF that is applied to the NV diamond.

The present inventors have realized that a configuration of RF elements can provide both the magnetic bias and the RF field for a DNV magnetic system. The magnetic bias provided by various implementations can be a uniform magnetic field along three polarizations of the axes of the coils used in various implementations. As described in greater detail below, using the various configuration of RF elements in a DNV sensor can allow greater access to the edges and faces of the diamond for light input and egress, while also providing a relatively uniform field in addition to a bias magnetic field. In various implementations, a NV diamond is contained within a housing. The housing can have six sides, each side operating as an RF element to apply a uniform RF field to the NV diamond. In addition, the six RF elements can also provide the magnetic bias for the NV sensor. Further, the six sides can be configured to allow various different configurations for light ingress and egress. The spacing and size of the RF elements allow for all edges and faces of the diamond to be used for light ingress and egress. The more light captured by photo-sensing elements of a DNV senor results in an increased efficiency of the sensor. In addition, the multiple polarization RF field of various implementations can increase the number of NV centers that are efficiently excited. In addition, the multiple polarization RF field can be used to differentially control the polarizations to achieve higher order functionality from the DNV sensor.

NV Center, its Electronic Structure, and Optical and RF Interaction

The nitrogen vacancy (NV) center in diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV⁰, while the negative charge state uses the nomenclature NV, which is adopted in this description.

The NV center has a number of electrons including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with ³A₂ symmetry with one spin state m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. In the absence of an external magnetic field, the m_(s)=±1 energy levels are offset from the m_(s)=0 due to spin-spin interactions, and the m_(s)=±1 energy levels are degenerate, i.e., they have the same energy. The m_(s)=0 spin state energy level is split from the m_(s)=±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_(s)=±1 energy levels, splitting the energy levels m_(s)=±1 by an amount 2gμ_(B)Bz, where g is the g-factor, μ_(B) is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct for a first order and inclusion of higher order corrections is a straight forward matter and will not affect the computational and logic steps in the systems and methods described below.

The NV center electronic structure further includes an excited triplet state ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. The optical transitions between the ground state ³A₂ and the excited triplet ³E are predominantly spin conserving, meaning that the optical transitions are between initial and final states which have the same spin. For a direct transition between the excited triplet ³E and the ground state ³A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

There is, however, an alternate non-radiative decay route from the triplet ³E to the ground state ³A₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m_(s)=±1 spin states of the excited triplet ³E to the intermediate energy levels is significantly greater than the transition rate from the m_(s)=0 spin state of the excited triplet ³E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³A₂ predominantly decays to the m_(s)=0 spin state over the m_(s)=±1 spin states. These features of the decay from the excited triplet ³E state via the intermediate singlet states A, E to the ground state triplet ³A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_(s)=0 spin state of the ground state ³A₂. In this way, the population of the m_(s)=0 spin state of the ground state ³A₂ may be “reset” to a maximum polarization determined by the decay rates from the triplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³E state is less for the m_(s)=±1 states than for the m_(s)=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_(s)=±1 states of the excited triplet ³E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_(s)=±1 states increases relative to the m_(s) =0 spin, the overall fluorescence intensity will be reduced.

NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System

FIG. 3 is a schematic illustrating a NV center magnetic sensor system 300 which uses fluorescence intensity to distinguish the m_(s)=±1 states, and to measure the magnetic field based on the energy difference between the m_(s)=+1 state and the m_(s)=−1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system 300 further includes an RF excitation source 330 which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330 when emitting RF radiation with a photon energy resonant with the transition energy between ground m_(s)=0 spin state and the m_(s)=+1 spin state excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_(s)=0 spin state and the m_(s)=+1 spin state, reducing the population in the m_(s)=0 spin state and reducing the overall fluorescence at resonance. Similarly resonance occurs between the m_(s)=0 spin state and the m_(s)=−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 spin state. At resonance between the m_(s)=0 spin state and the m_(s)=−1 spin state, or between the m_(s)=0 spin state and the m_(s)=+1 spin state, there is a decrease in the fluorescence intensity.

The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range which includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples, of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence.

In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results along with the known orientation of crystallographic planes of a diamond lattice allows not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

FIG. 6 is a schematic of an NV center magnetic sensor 600, according to an embodiment of the invention. The sensor 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620. The NV center magnetic sensor 600 may include a bias magnet 670 applying a bias magnetic field to the NV diamond material 620. Light from the NV diamond material 620 may be directed through an optical filter 650 and an electromagnetic interference (EMI) filter 660, which suppresses conducted interference, to an optical detector 640. The sensor 600 further includes a controller 680 arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630.

The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m_(s)=0 spin state and the m_(s)=±1 spin states as discussed above with respect to FIG. 3.

The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 610 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The EMI filter 660 is arranged between the optical filter 650 and the optical detector 640 and suppresses conducted interference. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610 and the RF excitation source 630. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610 and the RF excitation source 630 to be controlled.

According to one embodiment of operation, the controller 680 controls the operation such that the optical excitation source 610 continuously pumps the NV centers of the NV diamond material 620. The RF excitation source 630 is controlled to continuously sweep across a frequency range which includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of 2.87 GHz. When the photon energy of the RF radiation emitted by the RF excitation source 630 is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 or m_(s)=+1 spin state, the overall fluorescence intensity is reduced at resonance, as discussed above with respect to FIG. 3. In this case, there is a decrease in the fluorescence intensity when the RF energy resonates with an energy difference of the m_(s)=0 spin state and the m_(s)=−1 or m_(s) =+1 spin states. In this way the component of the magnetic field Bz along the NV axis may be determined by the difference in energies between the m_(s)=−1 and the m_(s)=+1 spin states.

As noted above, the diamond material 620 will have NV centers aligned along directions of four different orientation classes, and the component Bz along each of the different orientations may be determined based on the difference in energy between the m_(s)=−1 and the m_(s)=+1 spin states for the respective orientation classes. In certain cases, however, it may be difficult to determine which energy splitting corresponds to which orientation class, due to overlap of the energies, etc. The bias magnet 670 provides a magnetic field, which is preferably uniform on the NV diamond material 620, to separate the energies for the different orientation classes, so that they may be more easily identified.

FIG. 7 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. The magnetic sensor shown in FIG. 6 used a single RF excitation source 630 and a bias magnet 670. The DNV sensor illustrated in FIG. 7 uses six separate RF elements that also provide the bias field that is provided the bias magnet 670 in FIG. 6. Accordingly, in various implementations, the DNV sensor shown in FIG. 7 does not require a separate bias magnetic. FIGS. 7-13 illustrate various components of the DNV sensor.

In FIG. 7, the portion of the illustrated DNV sensor includes a heatsink 702 that can connect to the rest of the DNV sensor via a mounting clamp. Not shown is a light element, such as a laser or LED that is located within or near the heatsink 702. Light from the light element travels through a lens tube 706 through a focusing lens tube 718 and through a coil assembly 716 that includes the NV diamond. Light passes into the coil assembly 716 through the NV diamond and exits the coil assembly. Light that exits the coil assembly passes through a red filter to a photo sensor assembly 714. The coil assembly 716, red filter, and photo sensor can all be housed in a lens tube 710 that can be coupled to lens tube 718 via a lens tube coupler 708. A lens tube rotation mount 712 allows a rotation adjustment element to be attached that allows the coil assembly to be rotated in relation to the light element.

FIG. 8 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. The portion of the DNV sensor that is illustrated contains the coil assembly 816 and the photo sensor 820. The coil assembly 816 includes six RF elements. Each RF element has an RF mount that can be used to connect an RF cable 830. Thus, each RF element can have its own RF feed. In various implementations, the each RF element is fed a unique RF signal. In other implementations, sub-combinations of the RF elements receive the same RF feed signal. For example, groups of two or three RF elements can receive the same RF feed signal. Various connectors can be used to connect an RF cable 830 to the RF elements, such as a right angle connector 832. The coil assembly 816, red filter 826, EMI glass 824, and photo sensor mounting plate can be held in place using retaining rings 802. A photo sensor 820 can be secured to the photo sensor mounting plate 822, which can be used to locate the photo sensor 820 in the path of light that exits the coil assembly 816.

FIG. 10 is a cross section illustrating a coil assembly in accordance with some illustrative implementations. In this illustration, the light path 1030 is shown. The light path allows for light from the lighting element to pass through the coil assembly and through the NV diamond 1040. Light exits the NV diamond and proceeds out of the coil assembly through the light path 1030.

The coil assembly includes four RF elements 1002 and two top and bottom elements 1020. The NV diamond 1040 is held in place via a diamond plug 1004 that holds the diamond in the mounting block 1006. The RF elements can be held together using various means such as element mounting screws 1032. The six total RF elements can be seen in FIGS. 9A and 9B that illustrate a coil assembly in accordance with some illustrative implementations. Four side RF elements 902 are shown along with two top and bottom RF elements 920. Each RF element is attached to a center mounting block 904. Attachment mechanisms such as screws 932 can be used to attach the RF elements to the mounting block. In the illustrated implementation, a light injection hole 930 is the bottom RF element and the light exit hole 910 is in the top RF element. Accordingly, in this implementation light passes through the coil assembly and the diamond in a straight path. In one implementation, the light enters a face of the NV diamond and exits through another face of the NV diamond. As described below, in other implementation the light path through the coil assembly is not straight and may take on multiple paths of egress.

FIG. 11 is a schematic illustrating a side element 1100 of a coil assembly in accordance with some illustrative implementations. The side element 1100 can include a middle mounting hole and one other mounting hole. In this implementation, there would be side elements that had different mounting hole configurations. As shown in FIG. 11, the side element 1100 has three mounting holes, but not all mounting holes are required to be used. In one implementation, the middle mounting hole and one of the remaining two mounting holes are used, but all three mounting holes are not used. Each side element 1100 includes an RF connector 1102 that is used to provide the RF feed signal to the side element.

FIG. 12 is a schematic illustrating a top or bottom element 1200 of a coil assembly in accordance with some illustrative implementations. Similar to the side element 1100, the top or bottom element 1200 includes an RF connector 1202 for receiving an RF feed signal. The top or bottom element 1200, however, has only two mounting holes 1204. The three hole is a light path portion 1230 that allows for light to enter or exit the coil assembly.

FIG. 13 is a schematic illustrating a center mounting block 1300 of a coil assembly in accordance with some illustrative implementations. The NV diamond is located within the mounting block 1300. In one implementation, a diamond plug can be used to hold the NV diamond. The mounting block 1300 can include a diamond mounting location that provides alignment of the NV diamond. For example, the mounting block 1300 can include a recess that fits the NV diamond. Once positioned, the diamond plug can be inserted into the mounting block 1300 to hold the diamond in place.

FIGS. 14-17 illustrate another implementation. FIG. 14 is a cross section illustrating of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. A coil assembly 1416 holds an NV diamond within an NV diamond sensor. The coil assembly 1416 can include six RF elements, four side elements and two top and bottom elements (shown in FIGS. 15-17). RF cables 1430 can connect to the RF elements via RF connections 1432. The RF cables 1430 are used to provide an RF signal to one or more of the RF elements. The RF signal can be different for each RF element or subsets of the RF elements can receive different RF signals. These RF feed signals are used by the RF elements to provide a uniform microwave RF signal to the NV diamond. In addition, the arrangement of the RF elements allows the RF elements to also provide the magnetic bias field to the NV diamond. In the illustrated implementation, light enters and exits through the top and bottom elements. Light that exits the NV diamond can pass through a red filter 1426 and through a light pipe 1450 that is located within an attenuator 1440. In various implementations, at least a portion of the light pipe 1450 is located within the attenuator 1440. Such a configuration allows the photo-sensing array 1420 to be positioned closer to the NV diamond and remain unaffected by the EMI of the sensor. Further description of the benefits of housing a portion of the light pipe within an attenuator is described in U.S. patent application Ser. No. 15/003,281, entitled “Magnetometer with Light Pipe,” filed on the same day as this application, the contents of which are hereby incorporated by reference. Retaining rings 1402 can be used to hold the various elements together and in position.

FIG. 15 is a schematic illustrating a coil assembly in accordance with some illustrative implementations. FIG. 16 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations. The coil assembly includes two bottom or top RF elements 1506 and 1606. In the illustrated implementation, the top or bottom RF elements are circular and are larger compared to the side elements 1502 and 1602. In between the top or bottom elements are the four side elements 1502 and 1602. FIG. 17 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations. The side element has an RF connector 1702 used to provide a feed RF signal to the RF element. The side RF elements do not include any mounting holes as the side RF elements can be held into position by the top and bottom RF elements. In various implementations, each of the RF elements can include multiple stacked spiral antenna coils. These stacked coils can occupy a small footprint and can provide the needed microwave RF field in such that the RF field is uniform over the NV diamond. Additional details regarding RF elements and RF circuit boards that contain RF elements are described in U.S. patent application Ser. No. 15/003,309, entitled “DIAMOND NITROGEN VACANCY SENSOR WITH DUAL RF SOURCES,” filed on the same day as this application, the contents of which are hereby incorporated by reference. In various implementations, each RF side element and top and bottom RF elements can include an RF element or an RF circuit board.

The NV diamond 1622 is located within the six RF elements. The RF elements can be held together by mounting screws 1510 and 1610. A light injection portion 1504 of the top RF element allows light to enter the coil assembly and enter the NV diamond. The bottom portion includes a corresponding light egress portion 1620. The NV diamond can fit within a mounting block 1608 and be held in position via a diamond plug 1624.

FIGS. 18-24 illustrate another implementation. In the illustrated implementation, light enters the NV diamond through an edge of the NV diamond and exits through multiple faces of the NV diamond. How light enters and exits the NV diamond is based upon the orientation of the NV diamond relative to the light source. Thus, in various implementations the NV diamond can be repositioned to allow light to enter and exit from edges, faces, and/or both edges and faces.

FIG. 18 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. Similar to other implementations, the DNV sensor includes a light source heatsink 1802 and 1902, a mounting clamp 1804 for the heatsink 1802, a lens tube 1806, a focusing lens tube 1818, a coil assembly 1816 located, and red filters and photo sensor assemblies 1814, and a lens tube rotation mount 1812 and 1912. FIG. 19 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. In this implementation, the light source is an LED 1906. In other implementations, other light sources, such as a laser, can be used. A thermal electric cooler 1904 can be used to provide cooling for the LED 1906. Light from the LED 1906 can be focused using lens 1918. The focused light enters the NV diamond that is located within the coil assembly 1916.

FIG. 20 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. In this figure, the NV diamond 2040 within the coil assembly can be seen. Light enters the edge of the NV diamond in this implementation and exits the NV diamond 2040 from two faces of the NV diamond 2040. The light the exits the NV diamond 2040 travels one of two light pipes 1914. In various implementations, at least a portion of the light pipe is located within an attenuator. The NV diamond 2040 can be held in place within the coil assembly via center mounting blocks 2050. The mounting blocks and the coil assembly can be held in place using retaining rings 2052. RF cables 2030 connect to the RF elements via RF connectors 2032 to provide an RF feed signal to the RF elements as described in greater detail below.

FIG. 21 is a schematic illustrating a coil assembly in accordance with some illustrative implementations. FIG. 22 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations. FIG. 21 shows four side elements 2014 and 2242 located between the top and bottom RF elements 2112 and 2212. The center mounting blocks 2108 and 2208 and retaining plate 2106 and 2206 are also shown. As describe above, light enters the NV diamond 2240 at an edge. The light reaches the NV diamond via a light injection opening 2101 and 2202. Light exits the NV diamond 2240 substantially orthogonal to the ingress path through two light exit holes 2110. A second light exit hole is opposite of the illustrated light exit hole 2110. In FIG. 22, the second light exit hold is behind the NV diamond 2240.

FIG. 23 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations. The individual side element includes an RF connector 2304 and a light egress portion 2302. The side element, however, does not include any attachment holes. Rather, the side elements can be held in place within the coil assembly using the top and bottom elements as illustrated in FIGS. 24A and 24B.

FIGS. 24A and 24B are schematics illustrating top and bottom elements of a coil assembly in accordance with some illustrative implementations. The top element includes slots 2406 for aligning and holding into position the four RF side elements. The light injection hole 2404 is also shown. RF connectors 2404 located on both the top RF element and the bottom RF element allow for separate RF feeds to be separately applied to the top and bottom RF elements.

The foregoing description is provided to enable a person skilled in the art to practice the various configurations described herein. While the subject technology has been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology. In some aspects, the subject technology may be used in various markets, including for example and without limitation, advanced sensors and mobile space platforms.

There may be many other ways to implement the subject technology. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these embodiments may be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the subject technology, by one having ordinary skill in the art, without departing from the scope of the subject technology.

Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of the subject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases

A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. 

What is claimed is:
 1. A magnetometer comprising: a magneto-optical defect center material with a plurality of magneto-optical defect centers; a first optical excitation source that transmits excitation light that excites at least a portion of the magneto-optical defect centers of the magneto-optical defect center material; a first photo sensor that receives generated light that is generated by the portion of the magneto-optical defect centers; a plurality of radio frequency (RF) elements spaced around the magneto-optical defect center material, wherein the plurality of RF elements generate a microwave signal that is substantially uniform over the magneto-optical defect center material and generate a magnetic bias field to the magneto-optical defect center material; and a processor operatively coupled to the first photo sensor, wherein the processor is configured to determine a magnitude of an external magnetic field based on a signal received from the first photo sensor.
 2. The magnetometer of claim 1, wherein the plurality of RF elements are spaced about the magneto-optical defect center material to form a cuboid shape, and wherein the magneto-optical defect center material is within the cuboid shape.
 3. The magnetometer of claim 1, wherein the plurality of RF elements is six RF elements.
 4. The magnetometer of claim 3, wherein the plurality of RF elements are arranged in a cube formation, and wherein the magneto-optical defect center material is within the cube formation.
 5. The magnetometer of claim 1, wherein a first RF element of the plurality of RF elements comprises an ingress hole through which the excitation light passes, and wherein a second RF element of the plurality of RF elements comprises an egress hole through which the generated light passes.
 6. The magnetometer of claim 5, wherein the excitation light passes through a first side of the magneto-optical defect center material, and wherein the generated light passes through a second side of the magneto-optical defect center material.
 7. The magnetometer of claim 6, wherein the first side of the magneto-optical defect center material and the second side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material.
 8. The magnetometer of claim 1, wherein a first RF element of the plurality of RF elements comprises a first ingress hole through which the excitation light passes, wherein a second RF element of the plurality of RF elements comprises a second ingress hole through which the excitation light passes, wherein a third RF element of the plurality of RF elements comprises a first egress hole through which at least a first portion of generated light passes.
 9. The magnetometer of claim 8, further comprising a second optical excitation source, wherein the first optical excitation source transmits a first portion of the excitation light and the second optical excitation source transmits a second portion of the excitation light.
 10. The magnetometer of claim 8, wherein a fourth RF element of the plurality of RF elements comprises a second egress hole through which at least a second portion of the generated light passes.
 11. The magnetometer of claim 10, wherein the excitation light passes through a first side of the magneto-optical defect center material and through a second side of the magneto-optical defect center material, and wherein the generated light passes through a third side of the magneto-optical defect center material and through a fourth side of the magneto-optical defect center material.
 12. The magnetometer of claim 11, wherein the first side of the magneto-optical defect center material and the third side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material, and wherein the second side of the magneto-optical defect center material and the fourth side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material.
 13. The magnetometer of claim 1, wherein each of the RF elements comprises an RF connection that is configured to receive a feed signal, and wherein the feed signal generates the microwave signal.
 14. The magnetometer of claim 13, wherein the feed signal further generates the magnetic field bias.
 15. The magnetometer of claim 14, wherein the feed signal for each of the RF elements is a different RF feed signal.
 16. The magnetometer of claim 1, wherein the magneto-optical defect center material is diamond material.
 17. The magnetometer of claim 1, wherein the magneto-optical defect centers are nitrogen vacancy centers.
 18. A device comprising: a magneto-optical defect center material with a plurality of magneto-optical defect centers; and a plurality of radio frequency (RF) elements spaced around the magneto-optical defect center material, wherein the plurality of RF elements generate a microwave signal that is substantially uniform over the magneto-optical defect center material and generate a magnetic bias field to the magneto-optical defect center material.
 19. The device of claim 18, wherein the plurality of RF elements are spaced about the magneto-optical defect center material to form a cuboid shape, and wherein the magneto-optical defect center material is within the cuboid shape.
 20. The device of claim 18, wherein the plurality of RF elements is six RF elements.
 21. The device of claim 20, wherein the plurality of RF elements are arranged in a cube formation, and wherein the magneto-optical defect center material is within the cube formation.
 22. The device of claim 18, wherein a first RF element of the plurality of RF elements comprises an ingress hole through which excitation light passes, wherein the excitation light excites at least a portion of the plurality of magneto-optical defect centers, and wherein a second RF element of the plurality of RF elements comprises an egress hole through which generated light passes, wherein the generated light is generated by the portion of the plurality of magneto-optical defect centers.
 23. The device of claim 22, wherein the excitation light passes through a first side of the magneto-optical defect center material, and wherein the generated light passes through a second side of the magneto-optical defect center material.
 24. The device of claim 23, wherein the first side of the magneto-optical defect center material and the second side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material.
 25. The device of claim 22, further comprising a photo sensor that receives at least a portion of the generated light.
 26. The device of claim 18, wherein a first RF element of the plurality of RF elements comprises a first ingress hole through which excitation light passes, wherein a second RF element of the plurality of RF elements comprises a second ingress hole through which excitation light passes, wherein the excitation light excites at least a portion of the plurality of magneto-optical defect centers, wherein a third RF element of the plurality of RF elements comprises a first egress hole through which at least a first portion of generated light passes, and wherein the generated light is generated by the portion of the plurality of magneto-optical defect centers.
 27. The device of claim 26, wherein a fourth RF element of the plurality of RF elements comprises a second egress hole through which at least a second portion of the generated light passes.
 28. The device of claim 27, wherein the excitation light passes through a first side of the magneto-optical defect center material and through a second side of the magneto-optical defect center material, and wherein the generated light passes through a third side of the magneto-optical defect center material and through a fourth side of the magneto-optical defect center material.
 29. The device of claim 28, wherein the first side of the magneto-optical defect center material and the third side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material, and wherein the second side of the magneto-optical defect center material and the fourth side of the magneto-optical defect center material are opposite sides of the magneto-optical defect center material.
 30. The device of claim 18, wherein each of the RF elements comprises an RF connection that is configured to receive a feed signal, and wherein the feed signal generates the microwave signal.
 31. The device of claim 30, wherein the feed signal further generates the magnetic field bias.
 32. The device of claim 31, wherein the feed signal for each of the RF elements is a different RF feed signal.
 33. The device of claim 18, wherein the magneto-optical defect center material is diamond material.
 34. The device of claim 18, wherein the magneto-optical defect centers are nitrogen vacancy centers.
 35. A method comprising: receiving, at each of a plurality of radio frequency (RF) elements, a feed signal; generating, by the plurality of RF elements, a microwave signal that is substantially uniform over a magneto-optical defect center material that has a plurality of magneto-optical defect centers; and generating, by the plurality of RF elements, a magnetic bias field that is applied to the magneto-optical defect center material.
 36. The method of claim 35, further comprising: passing excitation light though a hole of a first RF element of the plurality of RF elements, wherein the excitation light excites at least a portion of the magneto-optical defect centers; and transmitting generated light through a hole of a second RF element of the plurality of RF elements, wherein the generated light is generated by the portion of the magneto-optical defect centers.
 37. The method of claim 36, further comprising receiving, at a photo sensor, at least a portion of the generated light.
 38. The method of claim 35, wherein the receiving the feed signal comprises receiving a unique feed signal at each of the plurality of RF elements.
 39. The method of claim 35, further comprising: passing excitation light though a hole of a first RF element of the plurality of RF elements and through a hole of a second RF element of the plurality of RF elements, wherein the excitation light excites at least a portion of the magneto-optical defect centers; and transmitting at least a first portion of generated light through a hole of a third RF element of the plurality of RF elements, wherein the generated light is generated by the portion of the magneto-optical defect centers.
 40. The method of claim 39, further comprising transmitting a second portion of the generated light through a hole of a fourth RF element of the plurality of elements.
 41. The method of claim 39, further comprising receiving, at a photo sensor, the first portion of the generated light.
 42. The method of claim 41, further comprising: receiving, at a first photo sensor, the first portion of the generated light; and receiving, at a second photo sensor, the second portion of the generated light.
 43. The method of claim 35, wherein the magneto-optical defect center material is diamond material.
 44. The method of claim 35, wherein the magneto-optical defect centers are nitrogen vacancy centers. 